Conventional magnetic recording media, such as magnetic disks, which record and reproduce digital data through a magnetic head, are initialized one by one in a servo writer. For example, the servo writer writes positioning signals on a magnetic disk through a magnetic head incorporated in the servo writer. The magnetic disk is initialized to improve the servo tracking performance of the magnetic head.
A very precise tracking facilitates to accurately record a digital data signal on a predetermined track and reproduce the digital data signal from the predetermined track even when the track density of the magnetic disk used in a magnetic disk drive is high. Therefore, the very precise tracking facilitates to improve the recording capacity of the magnetic disk.
The positioning signals are recorded on a magnetic disk by a sector servo method or by an embedding servo method. In the magnetic disk that employs the sector servo method, each track is divided in the extending direction thereof into a plurality of sectors, and the positioning signals are written at the head positions of the respective sectors. In the magnetic disk that employs the embedding servo method, positioning servo signals are written in advance in the deep layer of the magnetic film and data signals in the surface layer of the magnetic film.
Japanese Unexamined Laid Open Patent Application H03(1991)-228219 discloses a magnetic disk including a nonmagnetic substrate having an uneven level pattern and a magnetic layer having concave regions and convex regions following the uneven level pattern of the nonmagnetic substrate, and magnetized in the different directions. This magnetic disk, on which a magnetization inversion pattern for reading out the signals is formed at the precision of the uneven level patterning, facilitates to improve the track density. For parallel magnetization of the magnetic disk described above, the concave regions and the convex regions of the soft magnetic layer are magnetized accurately in the respective predetermined directions by applying magnetic fields in the opposite directions using a magnetic head having a wide gap and a magnetic head having a narrow gap. Therefore, this magnetic disk facilitates easy manufacture thereof and improvement of the positioning accuracy. Protection and management of the recorded data are facilitated by recording the copyright data in the medium in advance as well as by using the uneven level pattern for the head positioning signals.
The perpendicular magnetic recording method, which facilitates increasing the line recording density, has been employed to realize high recording density on the magnetic disk. The perpendicular magnetic recording method records data by magnetizing the magnetic recording layer perpendicular thereto. The magnetic disk for perpendicular magnetic recording includes a soft magnetic layer with a high magnetic permeability formed below the magnetic recording layer so that the magnetic field generated from the magnetic head at the time of recording can be applied effectively perpendicular to the magnetic recording layer. Since the magnetic flux generated from the magnetic head localizes to the soft magnetic layer, a strong magnetic field is applied perpendicular to the magnetic recording layer. For obtaining a magnetic field strong enough to facilitate recording and for preventing signal distortion at the time of reproduction, it is necessary to orient the magnetization in the soft magnetic layer parallel thereto, especially toward the radial direction of the magnetic disk. The easy axis of magnetization of the soft magnetic layer is oriented parallel to the soft magnetic layer, especially to the radial direction of the magnetic disk, by applying a magnetic field or by such a method during the formation of the soft magnetic layer.
Japanese Unexamined Laid Open Patent Application H07(1995)-228219 discloses a higher recording density attained by combining the foregoing track density increase by the uneven level pattern on the substrate and the recording line density increase by the employment of the perpendicular magnetization method. Prior to using the magnetic disk, the concave regions and the convex regions of the magnetic recording layer are magnetized in the same direction (e.g., upward) by applying a relatively strong magnetic field perpendicular to the magnetic recording layer and, then, the convex regions are magnetized in the opposite direction (downward) by applying a relatively weak magnetic field in the opposite direction.
For improving the resolutions at the time of recording and at the time of reproduction corresponding to the improved recording density, it is necessary even for the perpendicular magnetic recording method to set the spacing or gap between the magnetic head and the magnetic recording medium to be narrower than several tens nm. Especially for improving the sharpness of the perpendicular magnetic field generated from the magnetic head at the time of recording, it is effective to narrow the spacing between the pole tip of the magnetic head and the soft magnetic layer, not only by narrowing the spacing between the magnetic head and the magnetic recording medium, but also by thinning the protection layer and the magnetic recording layer as much as possible. Since the magnetic flux generated from the magnetic head localizes to the soft magnetic layer almost without being attenuated, it is obviously very difficult not to invert the magnetization in the concave regions of the magnetic recording layer but to invert the magnetization in the convex regions of the magnetic recording layer even when an uneven level pattern is formed on the nonmagnetic substrate and the strength of the applied magnetic field applied is adjusted optimally.
Accordingly, there still remains a need to provide a perpendicular magnetic recording medium that obviates the problems described above. The present invention addresses this need.
The present invention relates to a perpendicular magnetic recording medium mountable on various kinds of magnetic storage, such as an external storage of a computer.
According to one aspect of the invention, the perpendicular magnetic recording medium includes a nonmagnetic substrate, a soft magnetic layer on the nonmagnetic substrate, a magnetic recording layer above the soft magnetic layer, and a protection layer on the magnetic recording layer. The magnetic recording layer has perpendicular magnetizations that extend perpendicular to the major surface or plane thereof and representing data signals. The nonmagnetic substrate has concave portions that form an uneven level pattern thereon. The concave portions can generate a magnetic flux for detecting a predetermined signal based on the magnetization in the region of the soft magnetic layer in the concave portion of the nonmagnetic substrate. Hereinafter, the region of the soft magnetic layer in the concave portion of the nonmagnetic substrate will be referred to as the xe2x80x9cconcave region of the soft magnetic layer.xe2x80x9d
The depth of the concave portion and the thickness of the soft magnetic layer are larger than at least the length and the depth of the concave portion, and the easy axis of magnetization in the concave region of the soft magnetic layer lies perpendicular to the major surface of the perpendicular magnetic recording medium due to shape magnetic anisotropy. The cross sectional area of the concave portion along the major surface of the perpendicular magnetic recording medium can be narrower toward the bottom thereof. The predetermined signal can be a head positioning signal or a signal indicating copyright data for example.
The magnetic recording medium according to the invention does not utilize the magnetization in the magnetic recording layer, but utilizes the magnetization in the concave regions of the soft magnetic layer, when the magnetic recording medium uses the uneven level pattern on the nonmagnetic substrate for the predetermined signal, such as a head positioning signal and a signal indicating the copyright data or other data. This specific feature of the magnetic recording medium according to the invention facilitates using the magnetic fluxes generated from the concave regions of the soft magnetic layer as the predetermined signals. When the concave portion of the nonmagnetic substrate has a predetermined shape, the magnetic flux generated from the concave region of the soft magnetic layer can be used as the predetermined signal since the easy axis of magnetization in the concave regions of the soft magnetic layer lies perpendicular to the soft magnetic layer due to the shape magnetic anisotropy.
Since the magnetization in the region of the soft magnetic layer outside the concave portions of the nonmagnetic substrate lies parallel to the soft magnetic layer, the magnetic head does not detect the magnetic flux from the region of the soft magnetic layer outside the concave portions. Therefore, only the magnetic flux from the concave region of the soft magnetic layer is detectable as a signal. Since the magnetic flux from the concave region of the soft magnetic layer is larger than the magnetic flux from the magnetic recording layer, the signals corresponding to the uneven level pattern are detected not by the state of magnetization in the magnetic recording layer, but by the state of magnetization in the soft magnetic layer.
The magnetic recording medium according to the invention having the structure as described above is advantageous since the magnetization in the concave region of the soft magnetic layer and the magnetization in the entire magnetic recording layer are oriented perpendicular to the major surface or plane of the magnetic recording medium (upward or downward) and the magnetization in the region of the soft magnetic layer outside the concave portions of the nonmagnetic substrate is oriented parallel to the soft magnetic layer (along the easy axis of magnetization) only by applying a magnetic field perpendicular to the plane of the magnetic recording medium (upward or downward) and by removing the magnetic field to magnetically write the signals corresponding to the uneven level pattern on the magnetic recording medium.